Is your heating system underperforming with cold spots on radiators, gurgling noises or fluctuating boiler pressure? These are common signs of air in the system, which can affect efficiency and increase your bills.
But why is there air in my central heating system? Air can get in through leaks, pressure fluctuations and poor maintenance and create air bubbles in the pipes that block the water flow. Understanding the causes of air in heating systems and how to get rid of it by bleeding radiators and heating system venting air techniques will get your system back to optimal performance.
Key Points
- Air can get into central heating systems through leaks, temperature fluctuations and poor installation or maintenance.
- Trapped air reduces heating efficiency, causes cold spots on radiators, increases energy consumption, and causes boiler strain.
- Bleeding radiators releases air bubbles in the pipes and gets even heat distribution.
- After bleeding, the boiler pressure may drop and needs to be adjusted with the filling loop.
- Airlocks in the system can prevent radiators from heating properly; simple troubleshooting can often fix them.
- Preventative maintenance such as checking for leaks, monitoring pressure, and balancing radiators minimises air problems in the heating system.
- Automatic air vents and regular system checks reduce the risk of air accumulation.
What causes air to get into your central heating system?
Common causes of air in heating systems
Air infiltration is a common problem with central heating systems, reducing efficiency and uneven heat distribution. But how does air get into a central heating system? Here are the main causes:
- Leaks in the system – Small leaks in pipes, radiators or valves allow air to get in over time and create pockets that affect water circulation.
- Installation and maintenance – When a heating system is filled or serviced, air can get trapped in the pipes if not properly vented.
- Pressure fluctuations – Expansion and contraction of water due to temperature changes can create a vacuum effect and pull in air.
- Faulty components – A faulty expansion vessel or automatic air vent can fail to release excess air and create air bubbles in the pipes.
Signs your system has an airlock or trapped air
Recognise the symptoms of air in the system before it causes major inefficiencies. Some warning signs are:
- Cold spots on radiators: If only the bottom of the radiator is heating up and the top is cold, air may be blocking the flow.
- Gurgling noises: Air pockets can cause strange noises in the pipes and radiators.
- Fluctuating boiler pressure: A sudden pressure drop can mean air infiltration.
- Reduced heating performance: If your home isn’t warming up as it should, air pockets might be restricting water flow.
- Persistent heating system air problems: If you have to bleed your radiators frequently, air is getting into the system.
How Air in the System Affects Heating Efficiency
Radiator Performance
Air in radiators stops water from circulating properly and reduces heating efficiency. Instead of radiating heat evenly, affected radiators develop cold spots, and the boiler has to work harder. This increases energy consumption and your bills.
Boiler and system longevity
Air trapped in a heating system can cause more than discomfort. It can lead to:
- Boiler wear and tear: Since air reduces efficiency, the boiler has to run longer to achieve the desired temperature.
- Corrosion risks: Oxygen in trapped air accelerates corrosion inside pipes and radiators and shortens the system’s lifespan.
- Pressure imbalances: Excessive air pockets can cause heating system troubleshooting for air issues like boiler pressure fluctuations or pump failure.
See also: How to Remove Air Pocket in Cooling System
How to bleed radiators to release trapped air
Tools needed to bleed a radiator
To remove air in radiators, you’ll need:
- A radiator key (or a flathead screwdriver for modern radiators)
- A small container to catch any water drips
- A towel or cloth to prevent spills
Step-by-step guide to bleeding radiators
Follow these steps to safely release air bubbles in heating pipes:
- Turn off your heating system and let the radiators cool.
- Find the bleed valve (usually at the top corner of each radiator).
- Insert the radiator key and turn it counterclockwise. You should hear a hissing sound as the air escapes.
- Wait for water to flow out steadily, then tighten the valve back.
- 5. Repeat for all radiators.
- Check the boiler pressure and adjust it if necessary.
Boiler Pressure After Bleeding Radiators
Why Boiler Pressure Drops
When you bleed radiators, some water is released with the air and the boiler pressure drops. If the pressure is too low, your heating system may not work efficiently.
How to Safely Increase Pressure
To restore pressure after air removal, follow these steps:
- Find the filling loop on your boiler.
- Open the valve slowly and let water enter the system.
- Monitor the pressure gauge until it reaches the recommended level (1-1.5 bar).
- Close the valve and check for leaks.
How to Remove an Airlock in the Heating System
How to Remove Airlocks Without a Plumber
An airlock in the system can block water flow and leave radiators cold. To fix:
- Bleed all radiators, starting with the one closest to the boiler.
- If the issue persists, turn on all hot water taps and open a cold tap for a short time. This will force air out of the pipes.
- If the airlock remains, try increasing and decreasing the boiler pressure to push air out.
When to Call a Plumber for Airlock Issues
If bleeding the system doesn’t resolve the issue, it could be due to a blockage, faulty pump or hidden leaks. Persistent air in the system can cause long-term damage and inefficiencies, so professional help is needed.
At ResTemp Solutions, we specialise in diagnosing and fixing airlocks, trapped air and pressure issues in central heating systems. With over 30 years of experience in heating, ventilation and air conditioning, we provide solutions for domestic and commercial heating systems in Cork. Our team ensures optimal comfort and energy efficiency by finding the underlying system faults and implementing long-term fixes.
How to Prevent Air from Entering Your System in the Future
Maintenance Tips to Avoid Trapped Air
To prevent air in the system, follow these tips:
- Check for leaks in pipes and radiator valves.
- Service your boiler annually to ensure proper air venting.
- Check pressure regularly.
- Use auto air vents to get rid of trapped air.
- Balance radiators for even heat.
Why Monitoring Pressure and System Health Matters
Ongoing air maintenance for your heating system is key to preventing air and efficiency. Regular checks will detect issues early and save you repair costs.
See Also: How To Vent Your House
Frequently Asked Questions About Air in Central Heating Systems
How Does Air Get Into a Central Heating System?
Air enters through:
- Leaks in pipes or valves
- Initial system filling (if not properly vented)
- Pressure changes causing vacuum suction
- Poor maintenance or faulty air vents
Why Do You Get Air in a Central Heating System?
Even though it’s a closed system, air can enter through:
- Small leaks that allow oxygen in
- Corrosion reactions releasing gases into the water
- Improper bleeding techniques
What Happens If You Have Air in Your Heating System?
An airlock in the system can cause:
- Cold spots on radiators
- Inefficient heating and higher bills
- Gurgling noises in pipes
- Fluctuating boiler pressure
How Often Do Radiators Need Bleeding?
Bleed radiators at least once a year. If you notice:
- Cold spots
- Gurgling noises
- Low boiler pressure
Then, it’s time to bleed them again.
How Can Air Get Into a Heating System?
Causes of air in heating systems:
- Leaks and poor sealing
- Temperature-related expansion/contraction
- Improper venting after repairs
How Do I Fix an Airlock in My Central Heating System?
- Turn off the heating and bleed all radiators.
- Check and adjust boiler pressure if needed.
- Use the tap method to flush out trapped air.
- Call a plumber if the airlocks persist.
Conclusion
Addressing air issues in your heating system quickly means better performance, lower bills and longer system life. Regular air troubleshooting in your heating system will save you repair costs. A well-maintained system runs efficiently and keeps your home warm.
